(a) Field of the Invention
The present invention relates to a method for regenerating a NOx absorbing catalyst. Particularly, the present invention is directed to a method for regenerating a NOx absorbing catalyst and recovering poisoning of the NOx absorbing catalyst thereby limiting an amount of exhausted NOx within a constant range by the NOx absorbing catalyst.
(b) Description of the Related Art
In a diesel engine vehicle, exhaust gas includes great quantities of minute particulate matters (PM), nitrogen oxides (NOx), etc. Various methods are used to reduce such PM, NOx, etc.
As such methods, the NOx PM reduction system (“NPRS”) reduces PM and NOx at the same time using a diesel particulate matter filter (“DPF”) and a lean NOx trap (“LNT”).
The DPF physically collects particulate matters in the exhaust gas of a diesel engine using a trap that removes the collected particulate matters by heating the particulate matters above the oxidizing temperature which is between 600° C. to 650° C. The rate of PM collection is more than about 70%.
The NOx absorbing catalyst is an exhaust gas purification catalyst which purifies nitrogen oxides in exhaust gas. The NOx absorbing catalyst absorbs nitrogen oxides passing through, and performs an exhaust gas purification function by converting the absorbed nitrogen oxides to nitrogen (N2). Accordingly, appropriate regeneration must be performed for continuous purification function of the NOx absorbing catalyst.
Meanwhile, the exhaust gas also includes sulfur oxide (Sox) in addition to NOx. The NOx absorbing catalyst absorbs not only nitrogen oxide but also sulfur components. If sulfur components are accumulated in the NOx absorbing catalyst, the method of purifying nitrogen oxides of the NOx absorbing catalyst is deteriorated. In order to solve this problem, a recovery of poisoning of the NOx absorbing catalyst of sulfur must be performed.
As such, in order to maintain the original function of the NOx absorbing catalyst, a regeneration method for performing a regeneration mode for NOx reduction and a poisoning recovery becomes important.
One example involves a technology adopting two NOx sensors upstream and downstream of the NOx absorbing catalyst. In this method, if the sensed or detected values of NOx of the two sensors are equal to each other, a regeneration mode is performed for a constant period so as to regenerate the NOx absorbing catalyst. However, this method has a drawback in that the precise control of an amount of exhausted NOx is impossible since the regeneration is performed only when the NOx absorbing catalyst excessively absorbs NOx. In addition, this method has a limitation that the sulfur poisoning cannot be exactly determined and the recovery of the poisoning is only periodic.
Accordingly, a method for suitably performing the regeneration mode and the poisoning recovery mode in order to obtain the original purification function of the NOx absorbing catalyst is necessary.